static JScrollPane jscroll_verticalExtend(final Component c) {
  ret swing(func -> JScrollPane {
    new JScrollPane sp;
    sp.setViewport(new JViewport {
      protected LayoutManager createLayoutManager() {
        ret new ViewportLayout {
          public void layoutContainer(Container parent) {
            JViewport vp = (JViewport)parent;
            Component view = vp.getView();
            Scrollable scrollableView = null;
    
            if (view == null) {
                return;
            }
            else if (view instanceof Scrollable) {
                scrollableView = (Scrollable) view;
            }
    
            Insets insets = vp.getInsets();
            Dimension viewPrefSize = view.getPreferredSize();
            Dimension vpSize = vp.getSize();
            Dimension extentSize = vp.toViewCoordinates(vpSize);
            Dimension viewSize = new Dimension(viewPrefSize);
    
            if (scrollableView != null) {
                if (scrollableView.getScrollableTracksViewportWidth()) {
                    viewSize.width = vpSize.width;
                }
                if (scrollableView.getScrollableTracksViewportHeight()) {
                    viewSize.height = vpSize.height;
                }
            }
            
            // XXX
            viewSize.height = max(viewSize.height, vpSize.height);
            // YYY
    
            Point viewPosition = vp.getViewPosition();
    
            /* If the new viewport size would leave empty space to the
             * right of the view, right justify the view or left justify
             * the view when the width of the view is smaller than the
             * container.
             */
            if (scrollableView == null ||
                vp.getParent() == null ||
                vp.getParent().getComponentOrientation().isLeftToRight()) {
                if ((viewPosition.x + extentSize.width) > viewSize.width) {
                    viewPosition.x = Math.max(0, viewSize.width - extentSize.width);
                }
            } else {
                if (extentSize.width > viewSize.width) {
                    viewPosition.x = viewSize.width - extentSize.width;
                } else {
                    viewPosition.x = Math.max(0, Math.min(viewSize.width - extentSize.width, viewPosition.x));
                }
            }
    
            /* If the new viewport size would leave empty space below the
             * view, bottom justify the view or top justify the view when
             * the height of the view is smaller than the container.
             */
            if ((viewPosition.y + extentSize.height) > viewSize.height) {
                viewPosition.y = Math.max(0, viewSize.height - extentSize.height);
            }
    
            /* If we haven't been advised about how the viewports size
             * should change wrt to the viewport, i.e. if the view isn't
             * an instance of Scrollable, then adjust the views size as follows.
             *
             * If the origin of the view is showing and the viewport is
             * bigger than the views preferred size, then make the view
             * the same size as the viewport.
             */
            if (scrollableView == null) {
                if ((viewPosition.x == 0) && (vpSize.width > viewPrefSize.width)) {
                    viewSize.width = vpSize.width;
                }
                if ((viewPosition.y == 0) && (vpSize.height > viewPrefSize.height)) {
                    viewSize.height = vpSize.height;
                }
            }
            vp.setViewPosition(viewPosition);
            vp.setViewSize(viewSize);
          }
        }; // new ViewportLayout
      }
    }); // new JViewport
    sp.setViewportView(c);
    ret sp;
  });
}

Began life as a copy of #1006014